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[Frama-c-discuss] Jessie - problem with an example

Hello Kerstin,

Le mer. 09 sept. 2009 10:31:23 CEST,
"Kerstin Hartig" <kerstin.hartig at first.fraunhofer.de> a ?crit :

>     behavior yes:
>       assumes data->a <= data->b + 10; 
>       assigns data->b;
>     ensures data->b <= data->a;
>  */
> void refresh(struct MyData* data)

I guess your issue lies here: there is no post-condition saying that
data->b is positive. We only know that it is less than or equal to
data->a (By the way, your indentation is a bit misleading: the ensures
relates only to the behavior 'yes', not to all behaviors).
It is thus not possible to conclude that data->b is positive in the
main loop after the call to refresh. Remember that function calls are
seen as some kind of black box and that the only things which are known
outside of the function body are the clauses of the contract.

-- 
Virgile Prevosto
Ing?nieur-Chercheur, CEA, LIST
Laboratoire de S?ret? des Logiciels
+33/0 1 69 08 71 83